This disclosure relates to articles for display cover glass applications having scratch-resistance and retained optical properties, and more particularly to articles that include an optical film structure comprising scratch resistance, wherein the article exhibits 85% or more average light transmittance over the visible spectrum. As defined herein, the phrase “visible spectrum” includes wavelengths in the range from about 380 nm to about 780 nm.
Cover articles are often used to protect critical devices within electronic products, to provide a user interface for input and/or display, and/or many other functions. Such products include mobile devices, such as smart phones, mp 3 players and computer tablets. Cover articles also include architectural articles, transportation articles (e.g., articles used in automotive applications, trains, aircraft, sea craft, etc.), appliance articles, or any article that requires some transparency, scratch-resistance, abrasion resistance or a combination thereof. These applications often demand scratch-resistance and strong optical performance characteristics, in terms of maximum light transmittance and minimum reflectance. Furthermore, some cover applications require that the color exhibited or perceived, in reflection and/or transmission, does not change appreciably as the viewing angle is changed. In display applications, this is because, if the color in reflection or transmission changes with viewing angle to an appreciable degree, the user of the product will perceive a change in color or brightness of the display, which can diminish the perceived quality of the display.
Known cover articles can often exhibit a variety of different types of scratches after use in harsh operating conditions. In some instances, a significant portion of those scratches are microductile scratches, which typically include a single groove in a material having extended length and with depths in the range from about 100 nm to about 500 nm. Microductile scratches may be accompanied by other types of visible damage, such as sub-surface cracking, frictive cracking, chipping and/or wear. Evidence suggests that a majority of such scratches and other visible damage is caused by sharp contact that occurs in a single contact event. Once a significant scratch appears on a cover article, the appearance of the product is degraded since the scratch causes an increase in light scattering, which may cause significant reduction in brightness, clarity and contrast of images on the display. Significant scratches can also affect the accuracy and reliability of touch sensitive displays. A portion of such scratches and other visible damage as described above may also be caused by multiple contact events (including reciprocating abrasion or wear). Thus, these scratches, and even less significant scratches, are unsightly and can affect product performance.
Single event scratch damage can be contrasted with abrasion damage. Abrasion damage is typically caused by multiple contact events, such as reciprocating sliding contact from hard counter face objects (e.g., sand, gravel and sandpaper). Abrasion damage can generate heat, which can degrade chemical bonds in the film materials and cause flaking and other types of damage to the article. In addition, since abrasion damage is often experienced over a longer term than the single events that cause scratches, the film material experiencing abrasion damage can also oxidize, which further degrades the durability of the film and thus the article. The single events that cause scratches generally do not involve the same conditions as the events that cause abrasion damage and therefore, the solutions often utilized to prevent abrasion damage may not also prevent scratches in articles. Moreover, known scratch and abrasion damage solutions often compromise the optical properties.
Accordingly, there is a need for new articles, and methods for their manufacture, which exhibit scratch resistance over a wide range of different types of scratches, abrasion resistance and good optical performance.